JP2017120373A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an excellent energy saving property and form high-quality images while maintaining the accuracy in controlling the temperature of a fixing member.SOLUTION: A fixing device comprises: heat-fixing means including a rotatably held fixing member 21, a heat source 23 that heats the fixing member, and a rotatable pressure member 22 that is in pressure contact with the fixing member to form a nip part; a cover member 50 that includes an opening 53 and blocks part of at least the heat-fixing means; first temperature detection means 27 that faces the fixing member in a non-contact manner through the opening 53; and blocking means (sensor attachment member 93) arranged on the outside of the cover member 50. The blocking means blocks at least part of the opening and has a blocking amount changing according to a temperature detected by the temperature detection means.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a fixing device such as a copying machine or a printer using an electrophotographic system, and an image forming apparatus using the same.

  As a fixing device used in various image forming apparatuses such as a copying machine, a printer, a facsimile, or a composite machine thereof, a fixing device having a thin fixing belt made of a metal base and an elastic rubber layer is known. In this way, by providing a thin fixing belt with a low heat capacity, the energy required for heating the fixing belt can be greatly reduced, and warm-up time (printing from room temperature such as when the power is turned on) can be performed. The time required to reach a predetermined temperature (reload temperature) and the first print time (the time from when a print request is received to when the printing operation is performed and the paper is discharged) can be shortened. .

  Conventionally, as an example of this type of fixing device, as shown in FIG. 13, a thin endless belt (fixing belt) 100, a heat source 300 and a plate-like nip forming member 500 disposed inside the endless belt 100, And a pressure roller 400 that forms a nip portion N by contacting the nip forming member 500 via the endless belt 100 (Patent Document 1). In this case, since the endless belt 100 can be directly heated by the heat source 300 at a place other than where the nip forming member 500 is disposed, the heat transfer efficiency is greatly improved and the power consumption is reduced. For this reason, it is possible to further shorten the first print time from the heating standby time.

  Due to recent demands for environmental problems, further power saving of the fixing device has been demanded. As conventional power saving measures, in addition to improving the heating method (Patent Document 1) and improving the heater control inside the fixing device (Patent Document 2), there are contrivances for improving the heat retention of the fixing device itself. There is something. As another power saving measure, Patent Document 3 and Patent Document 4 increase heat retention by suppressing heat radiation from the fixing device by closing the opening of the sheet passing path during the non-fixing operation. The fixing device has an opening other than the sheet passing path. In particular, the opening for the non-contact type sensor causes a local temperature decrease in the longitudinal direction, which affects not only energy saving performance but also image quality.

  A non-contact type sensor will be described. Conventionally, in an image forming apparatus, an unfixed image formed on a sheet is heat-fixed on a sheet surface by using a fixing unit (a fixing roller or a fixing belt) having a heat source. In this case, the control of the fixing temperature is very important for stabilizing the sheet transportability and the image quality. Therefore, in general, the temperature of the fixing unit surface is monitored using a temperature detection sensor, and the heat source is controlled. Appropriate heating control is applied.

  In the past, contact sensors such as thermistors have been widely used as temperature detection sensors. However, when a contact-type sensor is used, the surface condition (temperature distribution and wear level) of the fixing roller and the fixing belt changes only in the area in contact with the sensor. Easy to appear. Further, since minute toner stains adhering to the fixing roller and the fixing belt accumulate in the contact type sensor, there is a problem that when the accumulated stains are peeled off suddenly, the stains appear on the fixed image. .

  These problems need to be avoided in pursuit of higher image quality of the image forming apparatus, and non-contact sensors such as thermopile are becoming mainstream. However, since the non-contact type sensor is very expensive, if it is built in a fixing device that is supposed to be replaced as a consumable item, the price of the consumable item is directly affected. In addition, since it is a non-contact type, it must be arranged at a predetermined distance from the surface of the fixing roller or fixing belt, and when it is built in the fixing device, it is necessary to secure a corresponding space in the fixing device. is there.

  Due to the above circumstances, a general configuration of the apparatus is a system in which a non-contact sensor is provided on the apparatus main body side and the temperature of the fixing unit is detected through a detection opening provided in the cover of the fixing apparatus. In such a conventional configuration, the detected temperature may be affected by the air flow around the fixing device.

  This problem will be described with reference to FIGS. 2 and 4B. Air from the outside of the fixing device flows in from the detection openings 53 (531, 532) provided in the exterior member 50 (cover) of the fixing device, and the surface (detection area 53a) of the fixing belt 21 shown in FIG. ) Is locally cooled. The controller of the image forming apparatus applies heating control to the heat source 23 of the fixing device in an attempt to maintain the temperature of the cooled detection area 53a at the target temperature adjustment temperature, so that the temperature outside the detection area exceeds the target temperature. End up. Exceeding the temperature of the fixing device may cause sheet winding and excessive gloss of image quality. Further, since the temperature in the fixing device decreases in the standby state, the fixing means must be heated to a fixing possible temperature when a printing instruction is issued, which shortens the warm-up time and hinders energy saving.

  As described above, a decrease in local temperature resulting from the inflow of air from the detection opening deteriorates the heat retention of the fixing device and affects the image quality. In order to prevent local temperature drop, a configuration that always closes the detection opening with a non-contact temperature sensor is conceivable, but in such a configuration, the volatilized toner wax adheres to the non-contact sensor and the detection surface becomes cloudy. In addition, since the distance between the object to be detected and the sensor is short, an accurate temperature sensor cannot be obtained. Although it is conceivable to increase the cover of the fixing device so as to give a margin to the internal space, the size of the device is undesirably large.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a fixing device that can shorten the warm-up time even when the temperature is detected from the hole of the unit exterior.

  In order to achieve such an object, a fixing device according to the present invention includes a fixing member that is rotatably held, a heating source that heats the fixing member, and a rotatable member that presses the fixing member to form a nip portion. A heat fixing unit including a pressure member; a cover member having an opening and shielding at least a part of the heat fixing unit; and facing the fixing member or the pressure member in a non-contact manner through the opening. A first temperature detecting means that performs shielding, and a shielding means outside the cover member, the shielding means shields at least a part of the opening, and the amount of shielding changes depending on the temperature detected by the temperature detecting means. Features.

  According to the present invention, it is possible to form a high-quality image with excellent energy saving while maintaining the accuracy of temperature control of the fixing member.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating a schematic configuration of a fixing device mounted on the image forming apparatus. FIG. 3 is a block diagram illustrating an example of a main part of a control system that controls the fixing device. FIG. 2 is a diagram illustrating a schematic configuration of a fixing device. It is a figure which shows the drive of the shielding means of the opening part for a detection. FIG. 2 is a diagram illustrating a schematic configuration of a fixing device. It is a figure which shows the drive of the shielding means of the opening part for a detection. It is a figure which shows the drive of the shielding means of the opening part for a detection. It is a figure which shows the drive of the shielding means of the opening part for a detection. It is a figure which shows the drive of the shielding means of the opening part for a detection. It is a figure which shows the drive of the shielding means of the opening part for a detection. It is a flowchart which judges opening and closing by a shielding means. It is a figure which shows a prior art example.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

  First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.

  An image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the apparatus main body. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K has a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals. In the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C, The reference numerals are omitted.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, and a cleaning device. A backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a power source (not shown) is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an entrance of a waste toner container (not shown).

  A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2M, 2C, and 2K containing replenishing toner are detachably attached to the bottle container 2. A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7, and each development from each toner bottle 2Y, 2M, 2C, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 that stores paper P as a recording medium, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like are provided. Here, the recording medium includes thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet and the like in addition to plain paper. Although not shown, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. A discharge tray 14 for stocking sheets discharged outside the apparatus is provided on the upper surface of the printer main body.

Next, a basic operation of the printer according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the respective photoconductors 5 in the respective image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise by a driving device (not shown), and the surface of each photoconductor 5 is charged by the charging device 6. Are uniformly charged to a predetermined polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as the photoconductor 5 rotates, the toner image on the surface of each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on the surface of each photoreceptor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized by a neutralizing device (not shown), and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the transport path R is timed by the registration roller 12 and sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the surface of the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

  After that, when the toner image on the surface of the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the transfer electric field formed in the secondary transfer nip causes a transfer on the intermediate transfer belt 30. The toner images are transferred onto the paper P all at once. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the surface of the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

  Next, the configuration of the fixing device 20 will be described with reference to FIG. As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member that heats the side of the paper P on which an unfixed image is carried, and a nip between the fixing belt 21 and the fixing belt 21. A pressure roller 22 as a pressure member for forming the portion N, a halogen heater 23 as a heat source for heating the fixing belt 21, a nip forming member 24 disposed inside the fixing belt 21, and a nip forming member A stay 25 as a support member that supports 24, a reflection member 26 that reflects the light emitted from the halogen heater 23 to the fixing belt 21, and a non-contact type as a first temperature detection means that detects the temperature of the fixing belt 21. A temperature sensor 27 and a separating member 28 for separating the paper from the fixing belt 21 are provided. Although a plurality of halogen heaters 23 are described in the present embodiment, a single number may be used.

  Further, as described above, the first temperature detection unit 27 is attached to the main body of the image forming apparatus 1. However, in the present application, the first temperature detection unit 27 and the first temperature detection unit 27 will be described as a fixing device.

  The fixing device 20 includes a non-contact temperature sensor 27 described below, and the opening 53 included in the fixing device 20 can be shielded by a shielding means based on the detected temperature detected by the fixing device 20.

  FIG. 3 is a block diagram illustrating a hardware configuration of the image forming apparatus 1 including the first temperature detection unit 27. The control unit 200 as a control unit includes a controller unit 200a and an engine control unit 200b.

  The controller unit 200a includes a CPU, a ROM, a RAM, and the like, and is connected to the engine control unit 200b, the operation unit 151, the external communication interface unit 152, and the like. The controller unit 200a executes a control program incorporated in advance, thereby controlling the entire image forming apparatus 1 and controlling inputs from the external communication interface unit 152 and the operation unit 151. For example, the controller unit 200a receives an instruction input from the user input via the operation unit 151, and performs various processes according to the instruction input. Further, the controller unit 200a receives a print job (image forming job) command and image data from an external host computer device or the like via the external communication interface unit 152, and controls the engine control unit 200b to control the color image on the sheet. And an image forming operation for forming and outputting a monochrome image.

  The engine control unit 200b includes a CPU, a ROM, a RAM, and the like, and executes a control program incorporated in advance, thereby executing a printer engine (a plurality of printer engines for performing image forming processing) based on a command from the controller unit 200a. The image forming unit, the fixing device 20 and the like are controlled. For example, the engine control unit 200b controls the energization to the halogen heater 23 or rotationally drives the pressure roller 22 so that the temperature of the fixing belt 21 detected by the first temperature detection unit 27 becomes a predetermined target temperature. The pressure roller driving unit 129 which is a driving means for controlling the pressure roller is controlled.

  The engine control unit 200b controls the moving mechanism driving unit 167 as a driving unit for the shielding unit based on the temperature detected by the first temperature detecting unit 27. Instead of the temperature detected by the first temperature detecting means 27, the temperature detected by the ambient temperature sensor 102 as the second control temperature detecting means may be used.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 includes a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Or it is comprised by the release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer. When there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image and uneven glossiness may occur in the solid part of the image There is sex. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluorine rubber provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22. Alternatively, it is constituted by a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a contact / separation mechanism 60 described later and is in contact with the nip forming member 24 via the fixing belt 21.

  At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the apparatus main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away. In addition, the fixing belt 21 and the pressure roller 22 are not limited to being in pressure contact with each other, and may be configured to simply contact without pressing.

  Each halogen heater 23 is fixed to a side plate (not shown) of the fixing device 20 at both ends. Each halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the printer body. The output control is based on the detection result of the surface temperature of the fixing belt 21 by the first temperature detecting means 27. Based on. By such output control of the heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. In addition to the halogen heater, an IH, a resistance heating element, a carbon heater, or the like may be used as a heating source for heating the fixing belt 21.

  The nip forming member 24 includes a base pad 241 and a sliding sheet (low friction sheet) 240 provided on the surface of the base pad 241. The base pad 241 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22, and determines the shape of the nip portion N by receiving the pressure applied by the pressure roller 22. is there. The base pad 241 is supported by a stay 25 having both ends fixed to the side plate. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22.

  The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the function of preventing the nip forming member 24 from bending. In the present embodiment, the surface of the base pad 241 facing the pressure roller 22 is formed into a flat surface, and the nip portion N has a straight shape. By making the nip portion N into a straight shape, the pressure applied by the pressure roller 22 can be reduced. The shape of the nip portion N is arbitrary, and may be a concave shape in addition to the straight shape.

  The base pad 241 is made of a material that is hard to some extent to ensure strength and is made of a heat resistant material having a heat resistant temperature of 200 ° C. or higher. This prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature range and stabilizes the surface shape of the nip portion N, thereby stabilizing the output image quality. Examples of the material of the base pad 241 include polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), and polyether ether ketone (PEEK). In addition to a general heat resistant resin, it is possible to use a metal or ceramic.

  The sliding sheet 240 may be disposed on at least the surface of the base pad 241 that faces the fixing belt 21. As a result, when the fixing belt 21 rotates, the fixing belt 21 slides with respect to the low friction sheet, so that the driving torque generated in the fixing belt 21 is reduced, and the load due to the frictional force on the fixing belt 21 is reduced. The It is also possible to adopt a configuration without the sliding sheet 240.

  The reflection member 26 is disposed between the stay 25 and the halogen heater 23. In the present embodiment, the reflecting member 26 is fixed to the stay 25. Examples of the material of the reflecting member 26 include aluminum and stainless steel. By arranging the reflection member 26 in this way, the light emitted from the halogen heater 23 toward the stay 25 is reflected to the fixing belt 21. As a result, the amount of light applied to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the radiant heat from the halogen heater 23 from being transmitted to the stay 25 and the like, energy saving can be achieved.

  Although not shown, both end portions of the fixing belt 21 in the axial direction are held by belt holding members inserted on the inner periphery thereof. The two belt holding members are respectively attached to the side plates. In this way, by holding only both ends of the fixing belt 21 by the belt holding member, the fixing belt 21 is in a state where it can be freely deformed except for the nip portion N between the both ends. Further, as the nip portion N is made straight, a force is constantly applied to the fixing belt 21 to deform it into an elliptical shape.

  In addition, the fixing device 20 according to the present embodiment is devised in various configurations in order to further improve energy saving and first print time.

  Specifically, the fixing belt 21 can be directly heated at a place other than the nip portion N by the halogen heater 23 (direct heating method). In the present embodiment, nothing is interposed between the halogen heater 23 and the left portion of the fixing belt 21 in FIG. 2, and the radiant heat from the halogen heater 23 is directly applied to the fixing belt 21 in that portion.

  Further, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is made thinner and smaller in diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  In this embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are configured to be equal. However, it is not limited to this configuration. For example, the fixing belt 21 may be formed so that the diameter thereof is smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressure roller 22, the recording medium discharged from the nip portion N is easily separated from the fixing belt 21.

  As described above, as a result of reducing the diameter of the fixing belt 21, the space inside the fixing belt 21 is reduced. However, the stay 25 is formed in a concave shape bent at both ends, and the inside of the portion formed in the concave shape. By accommodating the halogen heater 23, the stay 25 and the halogen heater 23 can be arranged even in a small space.

  Further, in order to dispose the stay 25 as large as possible even in a small space, the nip forming member 24 is formed compact on the contrary. Specifically, the width of the base pad 241 in the sheet conveyance direction is formed to be smaller than the width of the stay 25 in the sheet conveyance direction. Further, in FIG. 2, the heights of the base pad 241 at the upstream end 24a and the downstream end 24b in the sheet conveyance direction with respect to the nip portion N or its virtual extension line E are h1 and h2, respectively, and the upstream end 24a. When the maximum height with respect to the nip portion N or the virtual extension line E in the portion of the base pad 241 other than the downstream side end portion 24b is h3, h1 ≦ h3 and h2 ≦ h3 are satisfied.

  With this configuration, the upstream end 24 a and the downstream end 24 b of the base pad 241 are not interposed between the bent portions on the upstream and downstream sides of the stay 25 in the sheet conveying direction and the fixing belt 21. Therefore, each bent portion can be disposed close to the inner peripheral surface of the fixing belt 21. As a result, the stay 25 can be disposed as large as possible in a limited space in the fixing belt 21, and the strength of the stay 25 can be ensured. As a result, it is possible to prevent the nip forming member 24 from being bent by the pressure roller 22 and to improve the fixing property.

  Further, in order to ensure the strength of the stay 25, in this embodiment, the stay 25 comes into contact with the nip forming member 24 and extends in the paper transport direction (vertical direction in FIG. 2), and the base portion 25a. And a rising portion 25b extending from the upstream and downstream ends of the paper conveyance direction toward the pressure direction of the pressure roller 22 (left side in FIG. 2). That is, by providing the stay 25 with the rising portion 25b, the stay 25 has a horizontally long cross section extending in the pressure direction of the pressure roller 22, and the section modulus is increased, so that the mechanical strength of the stay 25 is increased. Can be improved.

  In addition, the strength of the stay 25 is improved when the rising portion 25 b is formed longer in the pressing direction of the pressure roller 22. Therefore, it is desirable that the leading end of the rising portion 25 b is as close as possible to the inner peripheral surface of the fixing belt 21. However, during rotation, the fixing belt 21 may be shaken (disturbance in behavior) regardless of whether it is large or small. Therefore, if the leading end of the rising portion 25b is too close to the inner peripheral surface of the fixing belt 21, the fixing belt 21 is moved to the leading end of the rising portion 25b. There is a risk of contact. In particular, in the configuration using the thin fixing belt 21 as in the present embodiment, since the swinging width of the fixing belt 21 is large, care must be taken in setting the position of the leading end of the rising portion 25b.

  In this manner, the rising portion 25b is disposed long in the pressing direction of the pressure roller 22 by disposing the leading end of the rising portion 25b as close as possible to the inner peripheral surface of the fixing belt 21. Can do. Accordingly, the mechanical strength of the stay 25 can be improved even in the configuration using the small-diameter fixing belt 21.

  Hereinafter, the basic operation of the fixing device according to the present embodiment will be described with reference to FIG. When the power switch of the printer main body is turned on, power is supplied to the halogen heater 23 and the pressure roller 22 starts to rotate clockwise in FIG. As a result, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22.

  Thereafter, the paper P carrying the unfixed toner image T in the above-described image forming process is conveyed in the direction of the arrow A1 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 in the pressure contact state and It is fed into the nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the paper P by heat from the fixing belt 21 heated by the halogen heater 23 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The paper P on which the toner image T is fixed is carried out from the nip portion N in the direction of the arrow A2 in FIG. At this time, the paper P is separated from the fixing belt 21 by the front end of the paper P coming into contact with the front end 28 a of the separating member 28 with the separation gap g interposed between the front surface of the fixing belt 21. Thereafter, the separated paper P is discharged out of the apparatus by the paper discharge roller as described above, and stocked on the paper discharge tray.

  The basic configuration of the characteristic part of the present invention will be described below. In the fixing device 20 according to the present invention, as shown in FIG. 4, the fixing belt 21 and the pressure roller 22 are accommodated in the exterior member 50.

  The exterior member 50 includes an outlet-side opening 51 that faces the outlet of the nip N, an inlet-side opening 52 that faces the inlet of the nip N, and a detection opening 53 that faces the outer peripheral surface of the fixing belt 21. Have Except for these openings 51, 52 and 53, the space around the fixing belt 21 and the pressure roller 22 is basically sealed by the exterior member 50.

  A belt holding member (not shown) that supports both ends of the fixing belt 21, the halogen heater 23, and the nip forming member 24 are all attached to the side plate as described above. The separating member 28 is also attached to the side plate. By attaching the side plate to the exterior member 50 (or by forming it integrally with the exterior member 50), the fixing belt 21, the halogen heater 23, the nip forming member 24, and the separation member 28 are held by the exterior member 50. As shown in FIG. 4A, the cored bar 22a of the pressure roller 22 is rotatably supported by the exterior member 50 via a bearing (not shown). Therefore, the pressure roller 22 is also held by the exterior member 50.

  As shown in FIGS. 4B and 4C, the first temperature detecting means 27 as a non-contact type temperature sensor is disposed outside the detection opening 53 (531, 532) of the exterior member 50, and this detection is performed. The surface temperature of the fixing belt 21 can be detected through the opening 53 for use. In the embodiment, since there are two heat sources for heating the fixing belt 21, that is, the end heater and the center heater, two non-contact temperature sensors are used for each temperature control, and the fixing device 20 has two locations. A detection opening 53 is provided. Needless to say, the number of the detection openings 53 is not limited to this, and the detection target may be the pressure roller 22. In this case, the detection openings are provided on the pressure roller side.

The fixing belt 21 and the pressure roller 22 are configured to be relatively close to and separated from each other by the contact / separation mechanism 60. Separation mechanism 60, the pressing lever 61 is displaced to O ₁ as a fulcrum by rotation of the roller drive cam 65. When the fixing belt 21 and the pressure roller 22 are approached by the contact / separation mechanism 60, a nip portion N is formed at the pressure contact portion between them, and when the both are separated, the nip portion N is eliminated. In the following, a case where the pressure roller 22 is the movable side and the pressure roller 22 is configured to approach and separate from the fixing belt 21 on the fixed side will be exemplified.

  During the printing operation, the sheet enters the nip portion N, and the sheet and toner take heat from the fixing belt 21. Therefore, the temperature of the fixing belt 21 corresponding to the lowered temperature is detected by the first temperature detecting means 27, and the heating amount is determined. It is necessary to decide. For this reason, a cycle of temperature measurement and control is always required during the fixing operation. When the first temperature detection unit 27 is on the main body side of the image forming apparatus 1, a detection opening 53 is provided in the exterior member 50, and the temperature It needs to be ready for measurement.

  On the other hand, when the printing is finished and the image forming apparatus 1 is not printing such as in the standby state or the energy saving mode, the temperature of the fixing belt 21 is monitored and the necessity of always maintaining the predetermined temperature is lower than that at the time of printing. It is only necessary that the fixing belt can be quickly heated to a predetermined temperature when requested.

  As described above, since the exterior member 50 has the detection opening 53, the detection area 53a, which is the portion where the fixing belt 21 is exposed, is exposed to the outside air, and in the axial direction as shown in FIG. Compared with the part, the temperature is likely to decrease, and a temperature deviation occurs in the axial direction. Since the temperature is to be controlled according to the detection area 53a based on the output of the first temperature detection means 27, the portion 53b other than the detection area 53a is overheated.

  In addition, the presence of the detection opening 53 also reduces the heat retention effect of the entire fixing device and reduces energy saving. Therefore, it is preferable to close it in a state where temperature measurement is unnecessary. Therefore, it is possible to save energy that there is a configuration in which the detection opening 53 provided in the exterior member 50 that is a temperature detection region is closed in a timely manner.

(1) Sensor-integrated embodiment FIG. 5 shows a first embodiment in which the detection opening 53 is actually closed. Although the detection openings 531 and 532 are described as 53 for the convenience of the drawings, this embodiment can be applied to both the detection openings 531 and 532.

  As shown in FIG. 5A, the first temperature detection means 27 is provided in a sensor attachment member 93 having an opening, and measures the temperature of the fixing belt 21 from the detection opening 53. The sensor attachment member 93 is for attaching the first temperature detection means 27 to the exterior member 50. When the temperature of the fixing belt 21 is measured by the first temperature detection means 27, the sensor attachment member 93 is positioned at a predetermined distance from the exterior member 50.

  Here, the time of measuring the temperature is, for example, when a paper passing operation or the like is being performed. In the present embodiment, the first temperature detection unit 27 measures the temperature of the fixing belt 21, but may measure the temperature of the pressure roller 22. Further, the temperature of the fixing belt 21 or the pressure roller 22 may be measured by an ambient temperature sensor 102 that detects the temperature in the fixing device 20.

  A sensor is attached to a sensor attachment member 93 surrounded by a side other than the detection opening 53 side, and the detection opening 53 is closed by contacting the exterior member 50. If a part 101 that deforms and follows the fixing device 20 such as a heat-resistant sponge or rubber is provided at a portion that comes into contact with the exterior member 50 and is in close contact with the exterior member 50, it is possible to more reliably shield the outside air. Become. As an actual drive, a method of providing a motor on the main body side and finally rotating and moving the cam B or the like from the drive train can be considered. In addition to the cam B, a linear actuator is also possible.

  5A is a position where the detection opening 53 is not blocked, FIG. 5B is a position where the detection opening 53 is completely blocked, and FIG. 5C is an intermediate position thereof. This is a position where the heat retaining effect is higher than that in the position (a) where it is not closed, and the heat retaining effect is lower than the position where it is completely closed in FIG. 5 (b). The determination as to which position of the sensor attachment member 93 will be described later.

  FIG. 6 is a perspective view of the fixing device 20 having the sensor mounting member 93, and the first temperature detecting means 27 is omitted for convenience of the drawing. As described above, the sensor attachment member 93 is surrounded by sides other than the detection opening 53 (531, 532) side. In FIG. 6, the sensor mounting member 93 (931, 932) has a rectangular parallelepiped shape, but is not limited thereto, and may be a cylinder or a prism. Further, the shapes of the two sensor attachment members 931 and 932 may be different from each other.

(2) Sensor-Separated Type Example FIG. 7 shows Example 2 configured to close the detection opening 53 (531, 532). Although the detection openings 531 and 532 are expressed as 53 for the convenience of the drawing, this embodiment can be applied to both the detection openings 531 and 532. As shown in FIG. 7A, the support handle 91 of the shielding member 90 attached to the main body side rotates about the rotating body A, so that the first attached to the main body side as shown in FIG. The temperature detection means 27 and the detection opening 53 are blocked. As an actual drive, a method of using a motor on the main body side and moving from the drive train using a roller or the like can be considered.

  The rotation amount can be rotated so that the shielding member 90 shields or does not cover the detection opening 53, and the cover amount can be halved as shown in FIG. 7C. .

  Further, as shown in the perspective views of FIGS. 8A and 8B, the support handle 91 of the shielding member 90 attached to the main body side rotates about 90 ° about the rotating body A, so that The structure which shields between the attached 1st temperature detection means 27 and the opening part 53 for a detection may be sufficient.

  At this time, if the elastic member 100 is provided on the exterior member side of the shielding member 90 and the height of the shielding member 90 is variable using the eccentric cam C installed on the main body side of the support handle 91 as shown in FIG. The adhesion between the member 90 and the exterior member 50 is improved, and the inflow of outside air can be prevented more reliably.

  A third embodiment configured to close the detection opening 53 will be described with reference to FIG. As shown in FIG. 10A, a foldable wall portion 92 provided on the main body side is connected to the fixing device 20 to block outside air. In this embodiment, a bellows-like wall portion is used as the foldable wall portion 92. The wall 92 extends as shown in FIG. 10B to shield the detection opening 53. The extension method may be a cam or the like, but is not limited thereto, and can be extended by a magnetic force. In this case, the wall 92 is made of a material having magnetic force, and the electromagnet characteristic is provided around the detection opening 53. When it is necessary to detect the detection opening 53, the wall 92 is extended by applying a magnetic force around the detection opening 53 so that a magnetic force is applied around the detection opening 53.

  FIG. 10C is a view of the wall 92 as seen from the detection opening 53 side. FIG. 10D is a perspective view of the wall portion 92. 10 (c) and 10 (d), the wall portion 92 is composed of three stages of small wall portions 92a, 92b, and 92c, but the number of small wall portions is not limited to this. The shape of the wall 92 is not limited to a rectangle, and may be a conical shape.

  Example 4 of the structure which closes the opening part 53 for a detection using FIG. 11 is demonstrated. In the fourth embodiment, the four sides of the first temperature detecting means 27 are surrounded by the wall portion 92. The wall 92 is bent at an angle. The bent portion of the wall portion 92 has a cam c, and the wall portion 92 rises toward the fixing device 20 by the rotation of the cam, so that the covering amount of the opening 53 can be adjusted. Although only one cam c is written because of the drawing, each wall portion 92 actually has a cam. Each cam can also move independently. In addition, since the 1st temperature detection means 27 is surrounded by the wall part 92, the 1st temperature detection means 27 is not illustrated in FIG.

  In the first to fourth embodiments, when there are a plurality of detection openings 53 corresponding to the first temperature detection means 27, the shielding member 90, the wall 92, and the sensor attachment member 93 (generally shielding means) are closed so as to block them. May be moved as a unit, or may be configured to move independently.

  Hereinafter, control for closing the detection opening 53 according to the present invention will be described with reference to FIGS.

  First, as indicated by S1, the controller unit 200a determines whether a print instruction (JOB) is input to the machine at the end of the printing operation (S2). When the print instruction is not input to the machine, the engine control unit 200b shifts to the standby mode S3.

  During non-printing, the shielding means covers the detection opening 53 and improves the heat retaining property of the fixing device 20, but the shielding means does not shield the detection opening 53 along with the transition to the standby mode (S4). The case where the atmospheric temperature output from the second temperature detecting means 102 or the first temperature detecting means 27 as the atmospheric temperature sensor in the fixing device 20 is 80 ° C. (hereinafter referred to as “closing threshold”) or more as a threshold, or to be detected When the temperature of the object is high, the standby mode is continued (S5), and the engine control unit 200b does not determine to block the detection opening 53. As a result, it is possible to prevent the temperature in the fixing device 20 from exceeding the heat-resistant temperature of each member, and to avoid the failure of the device and to keep the temperature of the device compatible.

  However, it may be difficult to determine whether or not the detection opening 53 should be blocked by the control based only on the ambient temperature. For example, when the temperature of the object to be detected is high, there is a high possibility that the ambient temperature will increase thereafter even if the ambient temperature is low. In such a case, the blockage threshold and the surface temperature of the object to be detected are used to determine whether or not the blockage is blocked and to determine the blockage amount.

  If the ambient temperature is equal to or lower than the closing threshold value in S4, the engine control unit 200b determines to drive the moving mechanism driving unit 167, and the moving mechanism driving unit 167 blocks the opening 53 (S6).

  After the opening 53 is covered by the moving mechanism driving unit 167, the first temperature detecting unit 27 or the second temperature detecting unit 102 detects the ambient temperature (S7). If the ambient temperature exceeds a threshold value (opening threshold value) after closing, the engine control unit 200b determines to drive the moving mechanism driving unit 167, and the moving mechanism driving unit 167 closes the detection opening 53. The state of being released is released (released) (S8). As a result, the temperature is lower than the closing threshold value before closing, but it is possible to prevent the apparatus from failing because the temperature exceeds the opening threshold value after closing. At this time, the opening threshold is preferably a temperature different from the closing threshold, and is set so that the opening threshold is higher. Although the opening threshold value is 90 degrees in the present embodiment, it can be appropriately changed in consideration of the thermopile and other durable temperatures.

  Here, “releasing the closed state” means releasing the completely closed state, and does not necessarily mean that the shielding means returns to the initial position. That is, intermediate states as shown in FIG. 5C and FIG. 7C are also included.

  The position of the intermediate state is determined as follows. When the atmospheric temperature detected by the first temperature detection means 27 or the second temperature detection means 102 reaches the open-time threshold value in the closed state, the moving mechanism driving unit 167 drives the shielding based on the atmospheric temperature, and When the temperature becomes equal to or lower than the opening threshold, the driving of the moving mechanism driving unit 167 is stopped. Thereby, heat insulation can be raised within the heat-resistant temperature range of the 1st temperature detection means 27 or the 2nd temperature detection means 102. FIG.

  It is possible not only to determine the intermediate state from the state of closing the opening 53 as described above, but also to determine the intermediate state from the initial state of not closing the opening 53. In that case, the engine control unit 200b drives the moving mechanism driving unit 167 based on the ambient temperature detected by the first temperature detecting unit 27 or the second temperature detecting unit 102 from the initial state, and the driving of the moving mechanism driving unit 167 The shielding means is moved to the detection opening 53 side, and the movement is stopped when the closing threshold is exceeded. And it can carry out by returning a shielding means to the position which does not exceed the threshold value at the time of closing.

  Even if the opening 53 is shielded by the shielding means, the temperature of the fixing belt 21 decreases with time. Therefore, in addition to the shielding of the opening 53 by the shielding means, it is also effective to warm the fixing device 20 by supplying power to the heat source at a certain time and lighting rate during standby.

  In the first exemplary embodiment, the first temperature detection unit 27 and the fixing belt 21 to be controlled are brought close to each other by the shielding unit to which the first temperature detection unit 27 is attached shielding the opening 53. If a thermopile is used as the first temperature detection means 27, the temperature may not be measured accurately due to the thermopile measurement principle.

  Therefore, a method of applying heat at regular intervals is conceivable, but it is difficult to keep the temperature at a certain target temperature without measuring the actual temperature of the fixing belt 21 during standby. Therefore, it is preferable to take a method in which the first temperature detection means 27 is moved away from the fixed time before heating and the temperature is measured and then heated. For example, it can be appropriately controlled to apply heat once every 10 seconds for 0.3 seconds.

In particular,
(1) The ambient temperature is measured by moving the non-contact temperature sensor 27 away from the object to be detected. (2) From the ambient temperature measurement result, the engine controller 200b determines the heating amount from a predetermined calculation rule ( 3) The engine control unit 200b instructs the moving mechanism driving unit 167 to drive, and the shielding unit shields the opening 53.
(4) Return to (1) again after a certain period of time. By controlling in this way, even the first temperature detecting means 27 that cannot measure the temperature normally because the distance to the controlled object is too close is not printed accurately. It becomes possible to control the temperature of the hour.

  Thus, in the present invention, the fixing belt 21 and the pressure roller 22 are accommodated inside the exterior member 50, and the detection opening 53 of the exterior member 50 can be opened and closed by the shielding means. While enabling detection, the detection opening 53 can be covered with a shielding means except during fixing to suppress heat dissipation from the fixing member 21 and enhance the heat retaining effect. Therefore, it is possible to reduce power consumption for reheating the fixing belt 21 when a print job is given while waiting.

  The present invention is not limited to the fixing device in which the fixing belt is thinned and reduced in diameter to improve energy saving and the like as in the above-described embodiment, but a known fixing device including a heating method using electromagnetic induction is used. It is possible to adapt widely. Further, the fixing device according to the present invention is not limited to the color laser printer shown in FIG. 1, and can be mounted on a monochrome image forming apparatus, other printers, copiers, facsimiles, or complex machines thereof. . In addition, it goes without saying that various modifications can be made without departing from the scope of the present invention.

20 fixing device 21 fixing belt (fixing member)
22 Pressure roller (Pressure member)
23 Halogen heater (heating source)
24 Nip forming member 25 Stay (support member)
27 Non-contact temperature sensor (first temperature detection means)
28 Separation member 50 Exterior member (cover member)
51 Exit-side opening 52 Entrance-side opening 53 Detection opening 53a Detection area 60 Contact / separation mechanism 61 Pressure arm 65 Roller drive cam 90 Shield member 91 Support handle 92 Wall portion 93 Sensor mounting member 100 Elastic member 102 Atmospheric temperature sensor (Second temperature detection means)
N nip part P paper (recording medium)
R Transport path B, C cam

Japanese Patent No. 4875385 Japanese Patent No. 4423070 JP 2013-174859 A Japanese Patent Application Laid-Open No. 07-064422

Claims (9)

A fixing member held rotatably;
A heating source for heating the fixing member;
A rotatable pressure member that presses the fixing member to form a nip portion;
A heat fixing means including:
A cover member having an opening and shielding at least a part of the heat fixing unit;
First temperature detecting means facing the fixing member or the pressure member in a non-contact manner through the opening;
The fixing device according to claim 1, further comprising: a shielding unit provided outside the cover member, the shielding unit shielding at least a part of the opening, and the shielding amount varies depending on the temperature detected by the first temperature detection unit.   The fixing device according to claim 1, wherein the shielding unit shields the opening when an atmospheric temperature in the fixing device is equal to or lower than a predetermined temperature.   The fixing device according to claim 2, wherein the ambient temperature is detected by the first temperature detection unit.   The fixing device according to claim 2, further comprising a second temperature detection unit inside the cover member, wherein the ambient temperature is detected by the second temperature detection unit.   4. The shielding state is canceled when an ambient temperature detected by the first or second temperature detecting means is equal to or higher than a certain temperature after the opening has shielded the opening. Or the fixing device of 4.   The fixing device according to claim 1, wherein the release of the shielding state is performed in a stepwise manner.   The fixing device according to claim 1, wherein the shielding is not performed during a fixing operation.   The fixing device according to claim 1, wherein electric power is supplied to the heating source at regular intervals in the shielding state.   An image forming apparatus comprising the fixing device according to claim 1.